Treating hides



Patented Mar. 21, 1939 UNITED STATES $3 tiiigi't iiiiii'tt PATENT OFFICETREATING HIDES Erich Hansen, Hohokus, N. J., assignor to BuffaloElectro-Chemioal Company, Inc., Tonawanda, N. Y.

No Drawing.

3 Claims.

This invention relates to a method for improving the usefulproperties oftanned animal skins and hides, and more particularly to a process ofimproving the color and resilience of leather without adverselyaffecting the tensile strength thereof.

In the process of preparing leather as practiced heretofore, includingall operations as are conventionally used to convert the raw animal hideinto a finished product suitable for use where the product 'must possessa light color and withstand wear and tear, the tanner ordinarily hasdifliculty' in producing finished leathers of constant uniformity ofcolor, and matching is therefore difficult. Due to the varied origin ofeach hide, the tanner is always confronted with the problem ofworkingwith hides, the history and composition of which he knows very little,to produce a salable article possessing a substantially uniform grade orfinish with the possibility of matching hides with respect to color,feel, level, and tensile strength, among other characteristics.

Heretofore substantially all efforts to obtain uniformity of color intanned skins or hides have consisted in exposing the tanned skins tosunlight to obtain a sunbleach, the so-called natural bleach.Thlsproceeding is a purely arbitrary or rule of thumb method and it ispossible during such exposures to injure the tanned hides or skins sincetanned hides and skins are prone to dry out, with a resultant loss ofvaluable properties in the finished leather. Further, with adverseweather conditions, the task of producing a leather of light and evencolor is rendered extremely diflicult. In order to prevent the dryingout of the skins it has been necessary heretofore to impregnate thetanned skins with mixtures of fat liquors and even oils to preventdrying out and protect the tensile strength of the leather. While theskin is exposed to sunlight in the open the fat liquor or oil and dirt,soot, dust or other extraneous impurities depositing upon the skin,prevent uniform color elimination by the sunlight. All of these foreignmatters must finally be removed from the leather before it is suitablefor ultimate use.

Due to this sunlight method of treatment, efficient operations intanneries are seasonal, intermittent, and at best limited to a few goodweather months of the year. Since the average time of bleaching bysunlight is on the order of two weeks or more, although under'idealweather conditions, a bleaching can be effected within p wwv sApplication April 17, 1935, 5 Serial No. 16,930 x95 1.

(01. 8-411) fi J capacity must be available for" the 'rposure andstorage of the skins during this operation, this method of procedureincreases the investment necessary as well as the risk, a large capacitybeing necessary to insure continuous production. In any case, no matterhow long the skin might have been exposed to sunlight a uniform bleachthroughout the skin can never be obtained by sunlight bleaching. Uponsplitting the tanned and sun treated skin, the back side (the inner partof the skin before splitting) will have the original yellowish color, acolor impossible of elimination by this procedure and, therefore,leathers produced by sunlight treatment are useful on one side only, atleast insofar as desirability of color, and possibility of matchingcolor is concerned.

In accordance with the procedures of the present invention, the hide isshaken to remove the salt, naphthalene or the like, then brushed orcleansed to remove foreign matter in the usual way, the type oftreatment being selected in accordance with the particular hide and inac-v cordance with the type of leather to be produced. The hidethereafter is dehaired, and is therefore subjected to any suitabledepilatory, the selection of the type of depilatory or the method oftreatment for hair removal being governed by practical operatingconsiderations.

Subsequent to depilation the hide is tanned in conformity with usual andstandard tanning operations, as, for instance, bymeans of an alum or aformaldehyde tannage. Where skins are tanned they are at times dried andalways contain more or less oil or fat liquor. The dry tanned skins orthose skins containing no excess of oil or fat liquor are thereafterimmersed and soaked with an aqueous solution containingv active oxygenor oxygen evolving material. Where the skins contain an abundance of oilor fat liquor they are washed, as, for instance, in a suitable drum inorder to flush out the excess fat liquor, and in general warm water isemployed for this operation, that is, water having a temperature in theneighborhood of from about 90 to 115 degrees F. although water having ahigher temperature may be employed providing no adverse eifect isproduced in the leather, and thereafter treated with the oxidizingsolution.

The oxygen evolving solution preferably used is a fairly concentratedsolution of hydrogen peroxide. Generally the peroxide is poured upon thewet skins which absorb the peroxide so that a solution expressed fromthe skin would show a concentration of hydrogen peroxide of about 0.1 to20 volumes or higher depending upon the type of skin treated, althoughthe usual concentration will be from about 2 to 5 volumes. Theabsorption of the peroxide solution into the skin is generally completein about a half hour whereupon the skins, still impregnated with theperoxide solution, are stacked upon trucks or at the convenience of thetanner placed upon racks, and air dried for a period of from about 12 to20 hours depending upon the type of skin, the humidity, and otherfactors.

The bleaching of the skins is preferably carried out in acid or nearlyneutral solutions, i. e., solutions preferably of a pH of about 5 to '7.In general where soft, glovey leathers are desired, the pH of thesolution is maintained near '7 and the leather is most desirable asglove leather and possesses an enhanced resilience. In fact, in additionto the leveling of color, the resilient quality imparted to the leatheris the characteristic most desired in tanned skins used for gloves.Where it is desired to impart firmness to the leather, for instance,shoe leather, the peroxide is introduced into the leather under a lowerpH, for instance, in the neighborhood of 4 to 5.5.

The hides or skins after depilation are tanned by an oil orformaldehyde, alum or vegetable tan and are generally alkaline in natureand to obtain the desired pH a suitable acid, such as sulfuric acid orother acid is added to the hides and skins in such quantity that uponagitation the desired degree of acidity is obtained through out thehides. To the properly acidified hides the hydrogen peroxide solution isthen added. Where it has been determined what quantity of acid isrequired for a given quantity of hides, the acid may be added with theperoxide.

As another advantage of the process it may be mentioned that it ispossible to eliminate the coloring matter generally adhering to the rootholes of pigskin from which the bristles have been removed at theslaughter house or in the early stages of the tanning process. Thenormal color of the tanned pigskin at this stage of treatment isyellowish but the root holes are generally darker in color and somewhatunsightly thus detracting from the value of the skin. To eliminate thisdefect, the pigskin is immersed in a volume solution of hydrogenperoxide for a few minutes or until there is a surface penetration ofthe peroxide into the skin, the penetration being substantiallyimmediate where the leather is of prime grade and not overloaded withoil or fat liquor. The skin is then removed from the solution and driedfor one to two days at which time the darker spots caused by the higherpigmentation around the root holes have been leveled off and an evencolor appearance imparted to the pigskin. By regulating the time ofimmersion and the quantity of peroxide taken up by the skin, whiteleathers of very high resilience and tensile strength are produced,something impossible of achievement heretofore.

Example I About ten dozen tanned sheep skins containing substantially noexcess of oil or fat liquor, are soaked in about 130 gallons of waterand the pH of the solution adjusted to a pH of about 6.5 to 7.0 untilthe skin has assumed about the same pH as the solution itself. To thissolution about 3 gallons of 100 volume hydrogen peroxide is added andthe skins permitted to soak for a period of a half hour or more or untilthe peroxide has penetrated the skins, the skins removed and hung up fordyeing or stacked on trucks for about two days and subsequently dried.The finished skins are of excellent light color, all level as to colorand capable of being matched and of a high resilience and glovey feel.

Ewample II About 200 pounds of wet kidskins, freed of excess fat or oiland containing sufiicient water to just drip, that is, about 200 to 300%water, are placed in a drum and about 8 gallons of 100 volume hydrogenperoxide, acidified with the quantity of acid, such as sulfuric acid,sufiicient to produce a pH of about 6.0 to 6.5, added and the drumrotated to induce good contact and absorption of the peroxide in theskins at which time the skins are removed from the drum and air dried.These skins possess an even and level color and greatly enhancedresilience.

Example III 250 pounds of buckskin, substantially free of excess fat oroil are immersed and soaked in water and the pH maintainedjat about 5.8until the skins are well plumped. The plumping is usually performed in adrum andthen about 3 gallons of 100 volume hydrogen peroxide are addedand the drum rotated. After about one hour the skins are dried, forinstance, upon racks, and are white and well adapted for uses where goodstrength and ability to withstand deformation are required, as, forinstance, in uppers of shoes and the like. .1,

From the foregoing, it will be seen that this invention provides amethod of treating tanned skins to produce skins of high tensilestrength and of good level color. It will be understood that certain ofthe metallic peroxides as well as the per salts, evoking hydrogenperoxide in acid solutions, may be used for the same purposes ashydrogen peroxide, due correction being made so that chemical equivalentquantities are employed.

It is claimed:

1. The method of treating animal hides or skins which comprisesdehairing the hide or skin, immersing the hide or skin in an aqueousbath containing sulfuric acid in an amount suflicient to produce pHvalue of between about. 4 to 7 whereby the hide or skin is plumped andabsorbs sufficient acid from the bath to render the skin acid andthereafter immersing the plumped hide or skin in a solution containinghydrogen peroxide until the hide or skin is impregnated with the same,removing the hide or skin so impregnated and permitting the same to dryuntil a substantial proportion of the water has been eliminated and thehide or skin has been bleached to the desired extent.

2. The method of treating animal hides or skins which comprisesdehairing the hide or skin, immersing the hide or skin in an aqueoussolution containing sufficient acid to produce a pH value of about 4 to7 whereby the hide or skin absorbs sufiicient of the solution to renderthe same acid in reaction and thereafter adding to the bath an amount ofhydrogen peroxide suflicient to produce the proper color and level inthe skin when the same is dried, the pH value of the solution beingmaintained at less than about 7.

3. The method of leveling off the color of hides or skins which havebeen freed of hair which comprises treating the hide or skin with anacid WEOGIFI .a n e e W t e b m H p a g n w a h h M b S u w u G a thesame and then drying the hide or skin until 4 to 7 until the hide orskin is plumped and aba substantial proportion of the water has beensorbs suflicient acid from the bath to render the eliminated and thehide or skin bleached to the skin acid, treating the plumped hide orskin with desired extent. 5 an aqueous solution containing hydrogenperox- ERICH HANSEN.

ide whereby the hide or skin is impregnated with

